A variety of techniques are known for wet etching indium oxide-based coating films used in transparent electrically conductive films and the like, but aqueous solutions containing hydrochloric acid are often used as etching liquid compositions due to them being inexpensive and exhibiting good etching speed.
For example, Patent Document 1 discloses an etching liquid composition for an indium-tin oxide (hereinafter abbreviated to ITO in some cases), which contains ferric chloride and hydrochloric acid.
In addition, as an example of etching liquid that does not use hydrochloric acid, Patent Document 2 discloses an aqueous solution that contains cupric ions, an organic acid, halogen ions, an azole compound and a poly(alkylene glycol) as an etching agent for copper and copper alloys. Here, the poly(alkylene glycol) is used to suppress dissolution of an electrolytic copper plating layer and to facilitate etching of an electroless copper plating layer that is an electrically conductive undercoat layer.